The present invention relates generally to material handling work vehicles and, more particularly, to a lift arm structure for a work vehicle such as a front loader.
Work vehicles having a front material-handling tool are commonly used in agriculture or in the earth-moving construction industry. Typically the work vehicle includes a hydraulically operated lift arm structure having a pair of lift arms. A material-handling implement or tool is coupled to the front end of the lift arm structure to move materials around a farm or construction site. Such tools may include tilting buckets, fork lift arms, balers, claws, etc. The tools typically are raised or lowered by a single or a pair of hydraulic actuators such as hydraulic cylinders, which move the tool from one vertical position to another position.
The lift arm structure is thus used to engage, lift and carry loads. Typically for a front loader, a pair of load lifting arms are each pivotally connected at their rear or proximal ends to the work vehicle. Typically, each lift arm is provided with its own hydraulic actuator for cooperatively raising and lowering the lift arms. For some front loaders, another pair of hydraulic cylinders, or alternatively a single cylinder, mounted on the lift arm structure provides further functions for the tool, such as tilting or dumping.
Many lift arm structures include a vertical bend or knee having an obtuse angle at an intermediate position along the longitudinal extent of the lift arm. The knee in the lift arm allows clearance for the front tires to turn in or out and to move vertically due to the vehicle suspension without hitting the lift arm when the arm is in a vertically lower position.
A tool, such as a tilting bucket, is connected between the forward or distal ends of each pair of lift arms. Often these tools may be wider than the vehicle width, such as for example, wide loader buckets. These wider tools may require the lift arms to converge to the vehicle width at their proximal ends. Convergent arms also allow the operator to better see the back edge or corner of the tool relative to the ground, for example. However lift arms that fully converge directly in a straight line from the tool to the vehicle require a more complex connection to the tool, especially if the work vehicle uses an additional pair of hydraulic cylinders to function the tool. It would be desirable to construct a semi-convergent lift arm that has a parallel portion at the distal end of the arm for mounting the pair of tool functioning cylinders. However, such an arm may need both a vertical knee and a semi-convergent horizontal bend along the longitudinal extent of the arm.
During material handling operations, relatively high bending and torque stresses are repeatedly imparted to the lift arm structure. These stresses include bending stresses when a heavy load is picked up or a twisting torque stress when one side of a load is unbalanced and weighs more than the other side of the load. These stresses are a result of different load forces acting on the lift arm structure during the operation of the work vehicle.
The lift arm structure must be strong to withstand these stresses. Since the weight of the materials used to make the lift arm structure can reduce the lifting and load capacity of the tool, lift arms are often fabricated as hollow, multiple-walled structures. One known multiple-walled lift arm is a hollow arm fabricated from a single piece of metal that is formed into a three-sided, open bottom, U-shaped arm structure. Another known arm is formed by a closed four-walled arm structure. Another known arm is formed from two C-shaped channel pieces that are joined together to form a hollow, four-walled structure.
However, in order to provide a lift arm with the vertical knee configuration, the above known hollow arms must be fabricated as two separate longitudinal sections. The separate sections are then longitudinal butted together and joined. Often a metal plate is positioned over the joint and welded to each sidewall section to reinforce the joint. Fabricating, positioning and attaching these sections increases manufacturing costs.
It is common to provide reinforcing plates that are welded to the sidewalls at selected locations along the lift arm structure where pivot pins and actuators are attached. It is also known to provide a shaped debris deflecting member on the top of each lift arm to protect the lift arm from collecting falling debris
While the above known arm configurations add strength to the lift arm structure, they also increase the cost to manufacture the lift arm structure. Moreover, these structural features may not be readily adaptable to the semi-converging lift arm configurations increasingly needed for wider tools.
Thus, there is a need for a lift arm structure that is lightweight and yet resistant to bending and torque stress. Preferably two sidewall members can be fabricated from flat plate material that needs only minimal forming. Preferably a simple structural member can be easily and economically attached between the two side plate members to position and reinforce the two flat sidewalls. Preferably a top member can deflect debris.
There is also a need for a strong, lightweight arm cross-section that can be readily fabricated with both a vertical knee and a horizontal bend for a semi-convergent configuration. The hollow lift arm structure must readily allow for at least one and preferably two angular transitions. For example, the hollow arm structure must transition at the vertical knee as well as allowing horizontal angle transition along the longitudinal extent for semi-converging arms.
Thus, there is a need for a lift arm structure that is strong, lightweight, reinforced against bending and torsion stress, requires minimal fabrication and is readily assembled.
A lift arm structure is provided for a work vehicle including a pair of lift arms arranged on opposite sides of the work vehicle. Each lift arm has a first end pivotally coupled to the work vehicle and a second end for coupling to a tool. Each lift arm includes an inner side plate member, an outer side plate member, an elongated top tubular member and a bottom member. Each side plate member has a plurality of pivot orifices including at least one pivot orifice near each end of the side plate member and at least one intermediate pivot orifice located between each end of the side plate member. The elongated top member is attached between each of the parallel side members at the top edge of the side plate member so as to connect substantially along the entire length of each side plate member. A bottom member is positioned in a spaced relationship from the top member between each side member and is connected to each side plate member. The elongated top tubular member provides additional strength to the plate members to resist bending and torque loads. A traverse member is mounted between each lift arm and connected to at least one of the pairs of inner sidewall plate members and outer sidewall plate members of each lift arm. Each side plate member can be fabricated with an integral lift attachment portion to increase fatigue strength.
The preferred tubular configuration for the top tubular member is rounded, with a circular tube being the most preferred. The tubular member is preferably joined to the side plate members at the top edge of the plate members. The tubular member can be bent vertically to accommodate a vertical knee configuration and can be bent horizontally to accommodate a semi-convergent configuration. A tubular bottom member can also be provided to further increase the strength of the lift arm for bending and torque loads.
A method for manufacturing a lift arm structure for a work vehicle includes the following steps. A pair of lift arms is formed preferably by cutting a first side member and a second side member from a flat plate of material such as a metal plate. The members may be cut to have a vertical knee. The cut arms may then be bent horizontally to have a horizontal semi-convergent configuration.
A plurality of pivot orifices are fabricated near each end of each side plate member and at least one intermediate pivot orifice is provided between each end of each side plate member. A pivot boss is attached at each pivot orifice.
An elongated top tubular member is bent appropriately and attached between the first inner sidewall plate member and the parallel second outer sidewall plate member along substantially the entire length of the top tubular member at the top edge of the plate members. Also a bottom member is attached between the first side plate member and the second side plate member in a spaced relationship from the top tubular member. The bottom member is attached to each side plate member along the length of the bottom member. A traverse member is attached to at least one of the pair of sidewall plate members between a pair of lift arm members. The lift arm structure can then be mounted for pivotal rotational on the work vehicle.